FYI:
I know it's been a while since anyone has posted to this, but this seems to be the best thread for this issue, according to Google.
I just had the same thing happen.
I tried a firmware update, it hung and after waiting ~30 minutes I cycled power only to find the blank screen issue described here.
I just encountered a similar problem updating firmware on my Elegoo Mars 3D printer, and the solution was to use a flash drive of less than 16GB formatted to FAT32.
I decided to try this with my Weller WX2 soldering station and it worked. I was able to complete the update to v0.85.
I didn't need to flash it to an earlier level, just insert WX2_085.hex on a 4GB flash drive formatted to FAT32. I don't know if it's necessary, but I made sure that the hex file was the only file or folder on the drive. The LED built into the drive started flashing, indicating drive activity for about 20-30seconds, then the WX2 LCD dimmed slightly, indicating a reset, then I got the Weller WX2 splash screen showing firmware v0.85.